The Soviet Union, officially the Union of Soviet Socialist Republics, was a federal socialist state in Northern Eurasia that existed from 1922 to 1991 and was the largest country in the world. Nominally a union of multiple national Soviet republics, in practice its government and economy were highly centralized. It was a one-party state governed by the Communist Party, with Moscow as its capital in its largest republic, the Russian SFSR. Other major urban centers were Leningrad, Kiev, Minsk, Tashkent, Alma-Ata and Novosibirsk. It spanned over 10,000 kilometers east to west across 11 time zones and over 7,200 kilometers north to south. Its territory included much of Eastern Europe as well as part of Northern Europe and all of Northern and Central Asia. It had five climate zones such as tundra, taiga, steppes, desert, and mountains.
The USSR had its roots in the 1917 October Revolution, when the Bolsheviks led by Vladimir Lenin overthrew the Russian Provisional Government which had replaced the autocratic constitutional monarchy of Tsar Nicholas II during the February Revolution of the same year.